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Intern. J. Neuroscience
, 118:59–77, 2008
Copyright C
2008 Informa Healthcare USA, Inc.
ISSN: 0020-7454 / 1543-5245 online
DOI: 10.1080/00207450601042094
MODULATION OF COGNITIVE PERFORMANCE
AND MOOD BY AROMAS OF PEPPERMINT AND
YLANG-YLANG
MARK MOSS
STEVEN HEWITT
LUCY MOSS
Human Cognitive Neuroscience Unit
Division of Psychology
University of Northumbria
Newcastle upon Tyne, United Kingdom
KEITH WESNES
Human Cognitive Neuroscience Unit
Division of Psychology
University of Northumbria
Newcastle upon Tyne, United Kingdom
and
Cognitive Drug Research Ltd.
CDR House
Goring-on-Thames, United Kingdom
This study provides further evidence for the impact of the aromas of plant essential
oils on aspects of cognition and mood in healthy participants. One hundred and
forty-four volunteers were randomly assigned to conditions of ylang-ylang aroma,
peppermint aroma, or no aroma control. Cognitive performance was assessed using
the Cognitive Drug Research computerized assessment battery, with mood scales
completed before and after cognitive testing. The analysis of the data revealed
Received 19 July 2006.
Address correspondence to Dr. Mark Moss, Human Cognitive Neuroscience Unit, Division
of Psychology, Northumberland Building, University of Northumbria Newcastle upon Tyne, NE1
8ST, U.K. E-mail: mark.moss@unn.ac.uk
59
60 M. MOSS ET AL.
significant differences between conditions on a number of the factors underpinning
the tests that constitute the battery. Peppermint was found to enhance memory
whereas ylang-ylang impaired it, and lengthened processing speed. In terms of
subjective mood peppermint increased alertness and ylang-ylang decreased it, but
significantly increased calmness. These results provide support for the contention
that the aromas of essential oils can produce significant and idiosyncratic effects on
both subjective and objective assessments of aspects of human behavior. They are
discussed with reference to possible pharmacological and psychological modes of
influence.
Keywords aroma, cognition, memory, mood, peppermint, ylang-ylang
INTRODUCTION
Putative effects of various aromas on aspects of human behavior can be
traced back to ancient Greece, where the extracts of aromatic plants were
used for cosmetic, religious, and medical purposes. Today the popularity of
aromas for pleasure, relaxation, and in therapeutics is unabated and typified
in the ever popular application of aromatherapy (Tisserand, 1993). Valnet
(1986) documents the historical clinical use of aromatherapy as a treatment
for various mood-disorders and the introduction of “modern” aromatherapy in
Europe can be traced back to Rene-Maurice Gattefosse in the 1920s (Wartik,
1995). Proponents of aromatherapy claim complex and far-reaching benefits
of essential oils—extracted and highly refined fragrant substances produced
by some plants—with each oil purported to possess quite exclusive properties.
Despite such widespread belief in the beneficial properties of aromatherapy
among the populace however, there has to date been limited scientific research
into the validity of such reputed effects.
Within the relatively small body of investigative research that exists,
findings thus far indicate that the claims made for essential oils may indeed
have some validity. Regarding therapeutic subjective effects, Martin (1996)
reported decreases in anxiety levels in patients undergoing computerized-
axial-topography (CAT) scans while in the presence of ambient heliotropin,
a vanilla-like odor, relative to controls. Similarly, the sedative reputation
of lavender has been evidenced in studies of anxiety reduction and mood
improvement in a range of situations (Lorig & Schwartz, 1987; Ludvigson
and Rottman, 1989; Buchbauer et al., 1991; Lehrner et al., 2005). Itai
et al. (2000) compared the effects of lavender and hiba oil on female patients
with chronic haemodialysis and found hiba oil to significantly decrease mean
levels of anxiety and depression, where lavender was found only to exert
AROMAS, COGNITION, AND MOOD 61
a beneficial effect on anxiety alone. It is worth noting however that no
benefit was present in a study investigating the effect of aroma on anxiety
in pre-procedural abortion patients (Weibe, 2000). Further to investigations
of subjective mood, Brownfield (1998) reported that massage with topical
administration of lavender resulted in more pronounced analgesic effects than
massage alone among patients with chronic rheumatoid arthritis. In addition to
studies of sedative or relaxing aromas, peppermint, jasmine, and rosemary oils
have all shown arousing properties in keeping with their collective reputation
(Warm & Dember, 1990; Kovar et al., 1987).
Employing more objective dependent measures, Diego et al. (1998) found
electroencephalogram (EEG) readings to show increased beta-power following
lavender inhalation, implying neurological sedation and corroborating subjec-
tive reports of calmness, whereas jasmine has been demonstrated to produce
increased alpha-power in the frontal cortices, indicative of increased arousal
(Wartik, 1995). Furthermore, peppermint appears capable of reliably producing
small EEG and electromyogram (EMG) or muscular-conductance fluctuations
during REM and NREM sleep (Badia et al., 1990), a finding that is able to rule
out the possible effects of expectancy.
The long-believed possibility that essential oils may influence performance
in cognitive domains has also received some attention. Degel and Koster (1999)
found inhalation of lavender to improve letter counting and mathematical tasks,
relative to inhalation of jasmine, whereas both extracts impaired creativity
performance relative to controls. Furthermore, Degel et al. (2001) described
a beneficial effect of lavender and orange aromas on a measure of implicit
memory. Warm et al. (1991) reported both peppermint and muguet essences
increased performance on a sustained visual attention task. Ilmberger et al.
(2001) explored the psychological component of performance effects and
ventured interlinked correlations between subjective evaluation of substances
and corresponding expectations, relative to task performance. The authors
contend that their results clearly assign a high psychological component to
the effects of essential oil aromas. This is somewhat in contrast to the findings
of Itai et al. (2000) and Warm et al. (1991) who argue for independent effects
on cognition that are separate to mood changes and further suggests avenues
of effect independent of psychological beliefs and expectations. Moss et al.
(2006) found a complex pattern of relationships between induced expectancies
and aroma effects when investigating the influence of chamomile aroma on
cognition and mood. The findings support to some extent those previously
identified elsewhere for the impact of expectation on physiological measures
under aroma conditions (Campenni et al., 2004).
62 M. MOSS ET AL.
In a previous investigation, Moss et al. (2003) compared cognitive perfor-
mance across lavender, rosemary or control conditions using a computerised
assessment battery. Lavender was found to globally impair memory and reaction
times, whereas rosemary was found to improve the overall quality of long-term
memory. With regard to subjective mood states, both control and lavender
groups became significantly less alert than the rosemary group over the test
session. In apparent contrast, Field et al. (2005) report improved mathematical
computation speed following lavender exposure, however—an effect they
suggest is a result of improved mood and greater relaxation. In a more applied
setting Sakamoto et al. (2005) found that although sedating, lavender could
improve work performance when applied during rest sessions, possibly by
improving the quality of relaxation.
A recent assessment of the effect of ylang-ylang aroma on physiological
parameters and subjective state demonstrated a possible “harmonization” effect
illustrated through reductions in blood pressure and heart rate accompanied
by increases in alertness and attentiveness (Hongratanaworakit & Buchbauer,
2004). However, no assessment of cognitive functioning was made. The accrued
evidence therefore generally supports the proposal of substance-specific effects
on subjective state, physiological measures, and to some extent cognitive
performance. To extend knowledge in the area, this study attempted to
further assess the impact of peppermint (Mentha piperita), and ylang ylang
(Canananga odorata) essential oil aromas on a wide range of cognitive
performance measures and subjective mood.
MATERIALS AND METHODS
Participants
One hundred and forty-four undergraduates and members of the general public
volunteered to take part in this study. The composition of the three experimental
groups was: peppermint condition 24 females (mean age 24.4 years, SD 5.6), 24
males (mean age 24.7 years, SD 5.0); ylang-ylang condition 26 females (mean
age 22.8, SD 5.1); 22 males (mean age 24.3, SD 6.0); control condition 28
females (mean age 24.5, SD 6.3), 20 males (mean age 21.9 SD 8.3). Prior to par-
ticipation each volunteer completed a health questionnaire. All participants self
reported that they were in good health and none were excluded from the study.
Aromas
“Tisserand” pure essential oils (Tisserand Aromatherapy, Newtown Road,
Hove, Sussex, BN3 7BA) of peppermint and ylang-ylang were used to produce
AROMAS, COGNITION, AND MOOD 63
the ambient aromas. Four drops of the appropriate oil (or water in the control
condition) were applied to a diffuser pad for a “Tisserand Aroma-stream.”
The Aroma-stream was placed under the bench in the testing cubicles so as to
be out of sight, and switched on for five minutes prior to the testing of each
participant. Each aroma was above detection threshold and of approximately
equivalent strength for each testing session as assessed by an independent party.
Testing Cubicles
Each testing cubicle measured 2.4 m long ×1.8 m wide ×2.4 m high and were
maintained at a temperature between 18 and 22 degrees Celsius throughout the
testing sessions.
Cognitive Measures
A tailored version of the Cognitive Drug Research (CDR) computerized
assessment system (installed on Viglen genie computers) was employed to
evaluate cognitive performance. The CDR system includes a number of
measures that are specific to particular aspects of attention, working memory
and long-term memory. Stimuli are presented on a color monitor, and (with
the exception of word recall) responses are made using a simple response
module containing two buttons labelled “Yes” and “No” respectively. A suite
of programs controls all aspects of testing, including selection of appropriate
sets of stimuli for presentation and recording all responses.
The tests employed in this study were presented in the following order.
Word Presentation.
A series of 15 words is presented sequentially for one
second each with an inter-stimulus interval of one second. The words are a mix
of one two and three syllables.
Immediate Word Recall.
The computer display counts down sixty seconds
during which time participants write down as many of the words from the list
as possible. Recall is scored for number of correct words, and errors (words
not presented in the list).
Picture Presentation.
Twenty photographs are presented, with a stimulus
duration of 2 s each, and inter stimuli interval of 1 s.
Simple Reaction Time.
The word Yes is presented in the center of the screen.
The participant has to press the Yes button as quickly as possible. There are
64 M. MOSS ET AL.
50 trials and the intertrial interval varies randomly between 1 and 2.5 s. The
reaction time is recorded in ms.
Digit Vigilance.
A number is displayed constantly to the right of the screen.
A series of 240 digits is presented one at a time in the center at a rate of 80 per
minute; 45 match the constantly displayed digit. The participant has to press
the Yes button as quickly as possible every time the digit in the center matches
the one constantly displayed. Accuracy of response (%), reaction time (ms),
and number of false alarms are recorded.
Choice Reaction Time.
Either the word Yes or the word No is presented
in the center of the screen. The participant has to press the Yes or No button
as appropriate and as quickly as possible. There are 30 trials (25 “Yes” and 2
“No”) and the intertrial interval varies randomly between 1 and 2.5 s. Accuracy
(%) and reaction time (ms) are recorded.
Spatial Working Memory.
A schematic picture of a house is presented for
5 s. The house has nine windows in a 3 ×3 pattern, 4 of which are illuminated.
A series of 36 presentations of the same house in which just one window is
illuminated follow, and the participant has to respond Yes if the window was
one of the four lit in the original presentation, or No if it was not. Sixteen of
the stimuli require a Yes response and 20 a No response. Reaction time and
accuracy are recorded and a sensitivity index calculated.
Memory Scanning.
Five digits are presented singly at the rate of one every
second for the participant to remember. A series of thirty digits is then presented.
For each, the participant must press Yes or No according to whether the digit
is thought to be one of the five presented initially. Fifteen stimuli require a Yes
response and 15 a No response. This is repeated three times using a different
5 digits on each occasion. Reaction time is recorded and a sensitivity index
calculated.
Delayed Word Recall.
The computer counts down 60 s during which time
participants free recall as many of the words from the list as possible. Recall
is scored for number of correct words; and errors (words not presented in the
list).
Word Recognition.
The 15 words initially presented for the word recall
are presented again in random order interspersed with 15 new words. The
participant presses Yes or No each time to signal whether or not the word was
AROMAS, COGNITION, AND MOOD 65
from the original list. Reaction time and accuracy are recorded and a sensitivity
index calculated.
Picture Recognition.
The 20 pictures presented earlier are shown again in
random order interspersed with 20 similar new ones. The participant signals
recognition by pressing the Yes or No button as appropriate. Reaction time and
accuracy are recorded and a sensitivity index calculated.
“Pencil and Paper”.
Visual Analogue Scales, assessing subjective levels of
alertness, calmness, and contentedness, were presented prior to and following
the computerized tests. Participants are required to indicate their current state
by marking a line drawn between two bipolar adjectives. The entire battery
took approximately 25 min to administer.
Primary Cognitive Outcome Measures
The aforementioned measures were collapsed into four global outcome factors,
and two sub-factors derived from the battery by factor analysis, as previously
utilized (Kennedy et al., 2000, 2001; Wesnes et al., 1997, 1999, 2000).
Quality of Memory.
Derived by combining the percentage accuracy scores
(adjusted for proportions of novel and new stimuli where appropriate) from
all of the working and secondary memory tests—spatial working memory,
numeric working memory, word recognition, picture recognition, immediate
word recall, and delayed word recall (with adjustments to the total percentage
correct for errors on the latter two tasks). One hundred percent accuracy across
the six tasks would generate a maximum score of 600 on this index.
Examination of the factor pattern suggests that this global “quality of
memory” factor can usefully be further divided into two sub-factors: “working
memory” and “secondary memory”
Working Memory Sub-Factor.
Derived by combining the percentage accu-
racy scores from the two working memory tests—spatial working memory, and
numeric working memory. One hundred percent accuracy across the two tasks
would generate a maximum score of 200 on this index.
Secondary Memory Sub-Factor.
Derived by combining the percentage
accuracy scores (adjusted for proportions of novel and new stimuli where
appropriate) from all of the secondary memory tests—word recognition, picture
66 M. MOSS ET AL.
recognition, immediate word recall and delayed word recall (with adjustments
to the total percentage correct for errors on the latter two tasks). One hundred
percent accuracy across the 4 tasks would generate a maximum score of 400
on this index.
Speed of Memory.
Derived by combining the reaction times of the four
computerized memory tasks—numeric working memory, spatial memory,
delayed word recognition, and delayed picture recognition (units are summed
milliseconds for the four tasks).
Speed of Attention.
Derived by combining the reaction times of the
three attentional tasks—simple reaction time, choice reaction time, and digit
vigilance (units are summed milliseconds for the three tasks).
Accuracy of Attention.
Derived by calculating the combined percentage
accuracy across the choice reaction time and digit vigilance tasks with
adjustment for false alarms from the latter test. One hundred percent accuracy
across the two tasks would generate a maximum score of 100.
The contribution of individual task measures to each of these factors and
sub factors is illustrated schematically in Figure 1.
Subjective Mood Measure: The Bond-Lader Visual Analogue
Scales (Bond & Lader, 1974)
The 16 visual analogue scales of Bond-Lader were combined as recommended
by the authors to form three mood factors: “alert,” “calm,” and “content.”
Procedure
Participants were approached individually and asked if they would help in
the validation of a new cognitive test battery. No mention of aromatherapy or
essential oils was made. This deception was carried out in order to avoid the
possibility of expectancy effects contaminating the data. Recruitment took place
one week prior to testing and participants were randomly and unknowingly
allocated to one of the three conditions, peppermint, lavender, or no odor
(control). They were then given a time and day on which to attend the laboratory.
Testing took place in three different cubicles, and on three different days of the
week (Monday, Wednesday, and Friday) to avoid cross-contamination of odors.
On arrival at the lab each participant was once again reminded that they were
there to assist in the validation of the new test battery, and to try their best on
AROMAS, COGNITION, AND MOOD 67
Figure 1. Schematic representation of the CDR battery showing (from left to right) running order
of tasks, individual task outcome measures, and the composition of the four factors derived by
factor analysis. Arrows indicate that a task outcome measure contributes to the given factor “Speed
of Attention,” “Accuracy of Attention,” “Quality of Memory,” or “Speed of Memory.” Dotted
lines indicate contribution to both “Quality of Memory” and to either “Working Memory” (-.-)or
“Secondary Memory” (- - - -), respectively.
all the tasks. They were then asked to complete the mood scale to supposedly
assess if the tasks affected mood. Participants were then taken into the cubicle
where they completed the CDR battery followed by a second mood scale.
Finally they were debriefed regarding the true nature of the experiment, and
any questions answered. If any of the participants commented on the presence
of an odor prior to or during the testing session, the researcher dismissed it
with responses of the kind: “nothing to do with me” and “don’t know where it
came from.” No participants indicated at any time that they felt the odor had
affected them at all, or that they thought the study was investigating the effect
of odor on performance or mood.
68 M. MOSS ET AL.
Statistics
Scores from the individual task outcome measures were combined to form
the four global outcome measure factor scores and the secondary memory and
working memory factor scores. These and the individual task outcome measures
making up the factors were analysed using the statistical package Minitab 12
for Windows. The one way analysis of variance (Anova) followed by Tukey
pairwise comparisons was employed to identify where any differences between
the three conditions may have existed. Analysis of subjective mood was made
in a similar manner on the pre to post testing difference scores, reflecting any
changes in mood state due to exposure to the aromas and/or as a result of
completing the assessment battery.
RESULTS
The analyses of the individual task outcome measures that make up the factors
are presented in Table 1. The results described here will concentrate on the
primary cognitive outcome measures described earlier.
Quality of Memory Factor
An independent groups Anova revealed a significant difference between groups,
F(2,141) =6.21; p=0.003. Tukey post-hoc comparisons identified that the
peppermint condition (mean =381.91) scored significantly higher than both
the ylang-ylang condition (mean =336.08), p<0.01, and the control condition
(mean =351.1), p<0.05, (Figure 2a). No other significant differences were
found.
Secondary Memory Sub-Factor
An independent groups Anova revealed a significant difference between groups,
F(2,141) =3.90; p=0.022. Tukey post-hoc comparisons identified that the
peppermint condition (mean =204.69) scored significantly higher than the
ylang-ylang condition (mean =174.27), p<0.05, (Figure 2b). No other
significant differences were found.
Working Memory Sub-Factor
An independent groups Anova revealed a significant difference between groups,
F(2,141) =3.84; p=0.024. Tukey post-hoc comparisons identified that the
Tab le 1 . Effects of peppermint and ylang-ylang essential oils on individual task outcome measures from the CDR battery. The units are number of correctly
recalled items for the word recall tasks, milliseconds for the reaction times. The sensitivity indices are calculated using the non-parametric signal theory
index (SI) presented by Frey and Colliver (1973)
Outcome variable 1) Control Mean ±s.d.
2) Peppermint
Mean ±s.d. 3) Ylang-Ylang Mean ±s.d. Significant comparisons
Immediate word recall correct 5.62 ±2.09 6.10 ±2.41 5.30 ±1.91 2 vs. 3∗
Immediate word recall errors 0.51 ±0.38 0.54 ±0.71 0.48 ±0.55
Simple reaction time 248.29 ±33.78 248.17 ±44.26 270.21 ±39.56 1 vs. 3∗,2vs.3
∗
Number vigilance accuracy 94.86 ±7.56 96.94 ±6.59 92.10 ±10.53 2 vs. 3∗
Number vigilance false alarms 1.14 ±0.77 1.00 ±1.22 1.54 ±1.57
Number vigilance reaction time 380.26 ±32.63 367.72 ±41.88 394.92 ±48.03 2 vs. 3∗
Choice reaction time 398.86 ±53.14 390.11 ±61.02 411.62 ±63.71
Spatial memory sensitivity index 0.91 ±0.10 0.91 ±0.10 0.85 ±0.27
Spatial memory reaction time 888.9 ±248.0 904.8 ±424.1 1060.1 ±492.4
Numerical working memory
sensitivity index
0.83 ±0.11 0.87 ±0.12 0.85 ±0.14
Numerical working memory
reaction time
710.5 ±140.1 728.4 ±202.5 807.6 ±293.9
Delayed word recall correct 3.67 ±2.03 4.28 ±2.80 3.21 ±2.70
Delayed word recall errors 0.42 ±0.77 0.52 ±1.05 0.69 ±0.97
Word recognition sensitivity index 0.58 ±0.11 0.66 ±0.23 0.60 ±0.31
Word recognition reaction time 769.4 ±212.7 883.6 ±394.5 905.6 ±257.3 1 vs. 3∗
Picture recognition sensitivity
index
0.63 ±0.24 0.69 ±0.19 0.62 ±0.16
Picture recognition reaction time 845.7 ±183.6 914.7 ±235.0 970.8 ±233.0 1 vs. 3∗
∗p<0.05.
69
70 M. MOSS ET AL.
Figure 2. Effectsof peppermint and ylang-ylang on the cognitive factors derived from the CDR test
battery: (a) “Quality of Memory,” (b) “Secondary Memory,” (c) “Working Memory,” (d) “Speed
of Memory,” and (e) “Speed of Attention” (see text for details). Figures depict mean values. Error
bars represent standard deviations. ∗p<0.05; ∗∗p<0.01.
peppermint condition (mean =177.23) scored significantly higher than the
ylang-ylang condition (mean =161.81), p<0.05, (Figure 2c). No other
significant differences were found.
Speed of Memory Factor
An independent groups Anova revealed a significant difference between groups,
F(2,141) =6.08; p=0.003. Tukey post-hoc comparisons identified that the
control condition (mean =3152.1 ms) was significantly quicker than the
AROMAS, COGNITION, AND MOOD 71
ylang-ylang condition (mean =3785.7 ms), p<0.01, (Figure 2d). No other
significant differences were found.
Speed of Attention Factor
An independent groups Anova revealed a significant difference between groups,
F(2,141) =4.45; p=0.013. Tukey post-hoc comparisons identified that the
peppermint condition (mean =1006.0 ms) was significantly quicker than the
ylang-ylang condition (mean =1078.9 ms), p<0.05, (Figure 2e). No other
significant differences were found.
Accuracy of Attention Factor
An independent groups Anova revealed no significant differences between
groups, F(2,141) =2.79; p=0.065.
Subjective Mood Measures
Analysis of the pre-test ratings indicated no differences to exist between the
three conditions on any of the mood variables prior to the experimental session:
Alertness, F(2,141) =1.11; p=0.331. Contentedness, F(2,141) =0.48; p=
0.620. Calmness, F(2,141) =0.39; p=0.678. Subsequent analyses compared
post-test minus pre-test change in mood scores.
Alertness
An independent groups Anova revealed a significant difference existed between
groups, F(2,141) =3.33; p=0.039. Tukey post-hoc comparisons identified
that the peppermint condition produced a small increase in alertness (mean
change =0.74) compared to a decrease in the ylang-ylang condition (mean
change =–6.93), p<0.05, when participants had completed the test battery,
(Figure 3a). No other significant differences were found.
Calmness
An independent groups Anova revealed a significant difference existed between
groups, F(2,141) =5.49; p=0.005. Tukey post-hoc comparisons identified
that the ylang-ylang condition produced an increase in calmness (mean change
=1.92) compared to a decrease for both the control condition (mean change =
72 M. MOSS ET AL.
Figure 3. Effects of peppermint and ylang-ylang on change in self-rated mood as measured using
the Bond-Lader Visual Analogue Scales: (a) “Alertness” and (b) “Calmness.” Figures depict mean
change (post-test minus pre-test ratings) such that a positive change represents an increase on that
dimension over the test session. Error bars represent standard deviations. ∗p<0.05; ∗∗p<0.01.
–7.87) p<0.01, and the peppermint condition (mean change –5.47)
p<0.05, when participants had completed the test battery, (Figure 3b). No
other significant differences were found.
Contentedness
An independent groups Anova revealed no significant differences between
groups, F(2,141) =0.1.46; p=0.236.
DISCUSSION
The results of this study clearly support the contention that the aromas of
essential oils can modulate mood and cognitive performance in healthy adult
volunteers. Furthermore, the effects observed somewhat reflect the properties
historically attributed to the aromas of these essential oils. Ylang-ylang is
widely regarded as possessing sedative and calmative properties (Tisserand,
1993), and is commonly found in products aimed at aiding relaxation. Such
a proposition was supported by the increase in “calmness” reported here
by participants in the ylang-ylang condition compared to those in both
the control and peppermint conditions. The possible stimulating effect of
peppermint aroma was only partially supported. A significant difference in the
alertness mood dimension was isolated between the two aroma conditions, with
peppermint producing a small increase and ylang-ylang a decrease. However,
although the control condition also reduced alertness, when compared to
peppermint the difference did not quite reach significance (p=0.06). No
AROMAS, COGNITION, AND MOOD 73
effect was found on the contentedness dimension, although an increase might
have been hypothesized for either or both aromas.
This pattern of subjective mood results was broadly reflected in the effects
on the factors derived from the assessment of cognitive performance across the
three conditions. An aroma that increases alertness may be expected to enhance
cognitive performance, and one that increases calmness to impair it, albeit
not universally (e.g., Field et al., 2005). Peppermint produced a significant
improvement in overall quality of memory, compared to both control and
ylang-ylang conditions. This factor derives from the accuracy scores from
all the tasks of long term and working memory and the improvement versus
controls only existed when all these tasks were considered together in this factor.
If the secondary (long term) and working memory sub-factors are considered
separately, peppermint was only found to be significantly enhance performance
when compared to ylang-ylang. These differences appear to be a reflection
of the combination of the enhancement and impairing properties of the two
aromas, respectively. Interestingly, the improvement in accuracy of memory
for peppermint was not at the cost of speed. The speed of memory factor
indicated that ylang-ylang slowed reaction times significantly compared to
controls. Peppermint, however, produced no significant change in this factor.
The factors derived from the tests of attention revealed a similar pattern
of results. For the speed of attention factor, ylang-ylang produced the slowest
reaction times, significantly so when compared to peppermint that produced
the quickest. No significant differences were revealed between the conditions
for the accuracy of attention factor.
Peppermint has also been demonstrated to enhance performance on a range
of physical exercise tasks (Raudenbush et al., 2001). The authors propose
that the effects are due to the aroma producing a change in (an unidentified
dimension of) mood and consequently in the level of motivation of the
participants. Although a small increase in alertness was recorded for peppermint
aroma in the current study, this was not significant compared to controls. It is
therefore unlikely that the recorded improvement in memory performance was
due to changes in mood or motivation. In addition, if motivation had been
responsible it might have been expected to impact those tasks with a low
cognitive load, that is, reaction times. The data reveal that this was not the case,
with no significant differences existing between the peppermint and control
conditions for either the speed of attention or speed of memory factors.
If the influence of the aromas of essential oils on cognition is not a
consequence of changes in mood related to characteristics of the aroma itself,
then an alternative needs to be considered. A direct pharmacological action
74 M. MOSS ET AL.
would require the absorption of volatile compounds into the blood and their
subsequent activity at a neuronal level. Although the level of active compounds
that may be absorbed from an ambient aroma through the lungs and nasal
mucosa is low when compared to other modes of administration, monoterpene
components of rosemary have been detected in the blood of rodents exposed
to the vapors of this essential oil (Jirovitz et al., 1990, 1992; Kovar et al.,
1987). An attractive aspect of a pharmacological mechanism for the affect of
aromas on cognition is the concept of substance-specificity. Such a concept
would fit neatly alongside the results reported here, with each aroma delivering
a unique pattern of influence on the cognitive factors described. In support of
the pharmacological influence of plant-based compounds research has provided
evidence that is pertinent here. Wake et al. (2000) demonstrated that sage and
melissa possessed neuropharmacological activity. Specifically, on the nicotinic
and muscarinic acetylcholine systems in homogenate preparations of human
cortical cell membranes. There is of course a long-established link between the
cholinergic system and memory, and it may be the case that other plants such
as peppermint and rosemary also possesses such activity. Such a possibility
remains to be investigated further at a neurochemical level.
Recent work with animals also supports the proposal that volatile organic
plant constituents can have direct pharmacological effects on behavior and
physiology. Compounds that emanate from the leaves of certain deciduous
trees such as the oak have been collectively termed “green odour” and this
has been shown to attenuate stress induced activation of the hypothalamo-
pituitary-adrenal (HPA) axis in rats (Akutsu et al., 2002). Such activation results
in persistent hyperthermia, which is significantly diminished by inhalation of
green odor.
An interesting comparison can be made to the results of the current study
to those reported by Moss et al. (2003) regarding the effects of rosemary and
lavender aromas on the same cognitive and mood assessments. Lavender aroma
was found to produce decrements in performance on secondary memory, speed
of memory, and speed of attention compared to controls. In contrast rosemary
only significantly enhanced secondary memory performance. With regard to
mood rosemary increased alertness compared to lavender and controls, and
lavender and rosemary both increased contentedness compared to controls.
These effects bear similarities to, but importantly also distinct differences to the
patterns observed here. Such findings support the contention that each essential
oil may possess it’s own idiosyncratic pattern of influence. This would be
consistent with the aroma therapist’s view and may be a result of the proportions
and structure of the constituent volatile compounds.
AROMAS, COGNITION, AND MOOD 75
Indeed, from the data presented here and evidence from elsewhere it seems
plausible that the effects observed in studies of the aromas of essential oils may
be a result of a combination of pharmacological, cognitive, and emotional
effects. The area is still ripe for further investigation.
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